1. Field of the Invention
The invention relates to new photoresists, particularly photoresists that can be applied and imaged with reduced undesired outgassing and/or as thick coating layers. Preferred resists of the invention are chemically-amplified positive-acting resists that contain one or more photoacid generator compounds and a resin component.
2. Background
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate. A photoresist can be either positive-acting or negative-acting. Photoresist compositions are described in Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York, ch. 2, 1975 and by Moreau, Semiconductor Lithography, Principles, Practices and Materials, Plenum Press, New York, ch. 2 and 4.
Ion implantation techniques have been employed for doping semiconductor wafers. By this approach, an ion beam implanter generates an ion beam within an evacuated (low pressure) chamber, and the ions are directed and “implanted” to the wafer.
Significant problems arise however with current ion implantation methods. For instance, imaged coatings of current photoresists that serve as masking layers often exhibit significant “outgassing” of volatile materials as a result of the ion bombardment and low pressure processing conditions. Such outgassing will compromise processing conditions, including undesired modulating of the operating pressure of the reaction vessel, deposition of organic materials on the optical equipment, and the like.
Certain efforts have been made to address such outgassing. For example, U.S. Pat. No. 5,858,623 reports ion-pretreatmnent of a photoresist layer. That approach adds more processing time and costs and would not be applicable to many resist systems. U.S. Pat. No. 6,458,430 also reports an ion-pretreatment of a photoresist layer to attempt to minimize undesired outgassing during subsequent ion implantation.
U.S. Pat. No. 6,369,874 reports a so-called outgassing mitigation apparatus in which to conduct implantation processes. That approach also adds costs and necessitates use of additional equipment.
In certain processes for semiconductor wafer manufacture, use of a photoresist as a thick coating layer (e.g. at a dried (post soft-bake) thickness of 1 or 2 microns or greater is desirable. For instance, thick film photoresists are used for the formation of semiconductor bumps (protruded electrodes) and for rewiring. Highly useful thick film photoresists are disclosed in U.S. pat. application Ser. No. 2003/0027086 to Thackeray et al.
Many reported thick film compositions however are inadequate for current needs. For example, current compositions are designed for longer wavelength imaging such as 365 nm or other wavelengths in excess of 300 nm such as used with a quinone diazide photoactive component, rather than shorter wavelength imaging such as sub-300 nm particularly 248 nm, which is required to higher performance applications. See U.S. pat. applications Ser. Nos. 2003/0059706 and 2003/0039931.
It thus would be desirable to have new photoresists that could provide reduced outgassing, particularly under ion implantation processes. It also would be desirable to have new photoresists that could be effectively processed as thick films.